1. Field of the Invention
This invention relates generally to apparatus for exposing a photosensitive material to a video frame as represented by a video signal and, more particularly, to apparatus for fully exposing photosensitive material one line at a time to an image which is simultaneously scanned by a line scanner.
2. Description of the Prior Art
One approach to obtaining a photographic image of a color television image is to directly photograph the screen of a color television using color film. This approach will reproduce the subject matter in a way which, while satisfactory for some purposes, is of a quality much poorer than that of a direct photograph of the scene being televised in terms of resolution, color rendition, contrast, etc. Another well-known technique is to first divide the color television signal into its color separation video signals, i.e., the red, blue, and green video signals, then sequentially display these signals on a monochromatic CRT whose screen is photographed through filters in a way that synchronizes the color of the filter to the color of the video signal being displayed on the screen. In this technique, color film would be exposed through a red filter to the image on the screen on a monochromatic CRT while the red color separation image is displayed; through a blue filter while the blue color separation image is displayed on the CRT and through a green filter while the green color separation image is displayed. The exposure times will depend on the optics, the phosphors of the CRT and the type of color film; and, the proper exposure time can be determined by trial and error. While this technique represents an improvement over the quality of an image produced by merely photographing a still frame color video picture, the non-linear response of the CRT in terms of light intensity to input signal level and the non-linear characteristics of most film materials represent inherent deficiencies that will not produce an image approaching the quality of a direct photograph of the scene being televised.
An improved method for obtaining a photographic image of a video frame as disclosed in U.S. patent application Ser. No. 341,317, entitled "Constant Light Greyscale Generator for CRT Color Camera System", by Lawrence E. Alston, filed Jan. 21, 1982, in common assignment herewith discloses an arrangement wherein the inherent non-linear response of the CRT in terms of light intensity to input signal level is overcome by utilizing a two level electron beam approach wherein the number of horizontal two level electron beam line scans is modulated by the control signal that would otherwise be utilized to control the electron beam intensity. Although this approach is a substantial improvement over and above what had heretofore been done, it nevertheless still utilizes red, green, and blue filters which must be sequentially moved by mechanical apparatus into place to expose the film to red, green, and blue color separation signals.
Therefore, it is a primary object of this invention to provide a system for exposing a photosensitive material to a video signal representing the image to be photographed without having to provide apparatus for mechanically moving a plurality of mechanical filters in an ordered sequence to sequentially expose the photographic material to the red, green, and blue color separation signals.
It is a further object of this invention to provide a simplified system for exposing a photosensitive material to a video signal representing an image to be photographed wherein the photosensitive material is fully exposed one line at a time to the image as it is scanned by a line scanner.